Tracing feed rate steering control

ABSTRACT

An improved electronic tracing control for automatically steering the direction of the command feedrate vector to maintain a substantially zero quadrature error.

United States Patent [191 ,Wnse [4 51 Feb. 6, 1973 [54] TRACING FEEDRATE STEERING [56] References Cited CQNTROL UNITED STATES PATENTSInventor: Robert Wise, lroveland. Ohio 3,568,029 3 1971 Bollinger..3l8/578 m1 Assign: e- Mihmn Cinch ijfifill 33?? 5235131133.:iiiiiiililfiv Ohio 3,582,749 6/1971 Wenzel ..3l8/578 l 1971 r [22] filedy Primary Examiner-Benjamm Dobeck [2]] Appl. No.: l4591 Attorney-HowardT. Keiser et al.

57 ABSTRACT [52] U.S.-'Cl. 318/632, 318/39, 3l8/633 1 51 Int. Cl. ..G05b11/01 An improved electromc tracing control for automate [58] Field ofSearch I 318/578 633 6 39 callyvsteering the direction of the commandfeedrate I vector to maintain a substantially zero quadrature er- TOT.

4 Claims, 3 Drawing Figures X 30 I ,3 a 4 k T DEFL HFTN QUAD X-AXlS To XAXIS M ADJ ERROR CONT SCLIJR CIR GEN GEN DR'VE FDRT 42 PORT Y-AXIS ToFMS com) STEER CONT GEN I CONT 45 GEN DRNE T lage A8 TRACING CONTROL &8

PATENIEDFEB 6 I975 SHEET 2 OF 2 K m wmsE com mmjmEUD 2 Ill % 55552.mommw TRACINGFEED RATE STEERING CONTROL BACKGROUND OF THE INVENTION Theinvention relates general to the area of tracing controls; andspecifically, the invention provides an apparatus for improving theaccuracy of the path of a tracing finger as it traces the configurationof a model.

The invention is for use on a machine having a tracing head with atracking finger in contact with model. Transducers in the tracing headproduce deflection signals to a tracing control. The tracing controlproduces the appropriate drive signals to driving mechanisms on themachine for moving the tracing finger around the model. The generalconstruction and theory of operation of tracing controls are well-knownin the art, and a comprehensive detailed description of any particularcontrol will not aid the disclosure of the present invention. Applicantwill only briefly review the theory and detail only that portion whichis relevant to the present invention.

Generally, the tracing finger follows a cross section of the modelwithin a predetermined tracing plane. For simplicity, the tracing planewill be defined parallel to one of the orthogonal coordinate planes ofthe machine; and further, the tracing finger will be assumed to onlyexperience deflections within the tracing plane. Tracing heads aregenerally constructed with transducers producing deflections signalscoinciding with the coordinate axes of the machine. The deflectionsignals are received by the tracing control and combined to produce atracing error signal. The tracing error signal can also be considered tobe composed of two vectors within the tracing plane and existing at thepoint of contact of the tracing finger on the model, i.e., the tracingpoint. The first vector or feed rate vector is tangent to the model atthe tracing point and has a mag nitude representing a predeterminedvalue of velocity.

The second vector or quadrature vector is perpendicular to the model atthe tracing point and has a magnitude representing the error in theposition of the tracing finger relative to the model. In other words,the quadrature vector is responsible for maintaining the tracing fingerin constant contact with the model and therefore defines the accuracy ofthe tracing process. The tracing control must respond to the deflectionsignals from the tracing head and produce drive signals to the tracingmachine which maintain the tangential velocity of the tracing finger ata predetermined value while holding the deflection of the tracing fingerperwill be most apparent. One further related error is introduced whentracing fingers of different lengths are used. Each new tracing fingerlength will result in a new pendicular to the model to a predeterminedvalue, i.e.,

the hang free to null deflection.

In theory, most tracing controls are capable of accomplishing thisresult. However, there are certain variables which introduce tracingerrors as a result of the physical act of mechanically tracing over themodel. For example, friction between the tracing finger and the modelwill introduce error. The magnitude of friction is a function of thesurface finish and other conditions on the surface of the model. Anothersource of error arises from the varying spring constants in thetransducers in each directional axis within the tracing head. With mosttracing heads, this is especially a problem when tracing a model surfacethat is displaced 45 degrees from the axis of the'tracing finger. Sincethis geometry should produce equal deflections in two of the axes, anerror caused by unequal spring constants spring constant in thedirections perpendicular to the axis of the tracing finger.Consequently, the mechanical gain in each system changes, and errorsresult in the tracing output. A further source of error may arise frommechanical misalignments of thetransducers in the tracing head withrespect to the coordinate axes.

Each of the conditions above can introduce a slight rotation of the feedrate vector which is ideally produced tangent to the model at thetracing point. This non-tangential feed rate vector will cause thetracing control to stabilize with some quadrature error. In other words,the tracing control will maintain an orientation of the tracing fingeron the model which is displaced from the hang free to null position. Thedisplaced position of the tracing finger will cause a relativelyconstant oversize or undersize error in the tracing process.

Applicant discloses an improved tracing control for automaticallysteering the feed rate vector to its ideal tangential position, therebymaintaining the quadrature error at zero. Applicants apparatus isoperative re-- gardless of the cause of the feed rate vector rotationand therefore is free of the disadvantages discussed above.

SUMMARY OF THE INVENTION The present invention claims an improvedtracing control of the type producing an error signal represent- BRIEFDESCRIPTION OF THE DRAWINGS FIG. 1 is a general block diagram of atracing control containing the invention. FIG. 2 is blockdiagramillustrating the basic com ponents of the invention.

FIG. 3 is a detailed schematic diagram of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a general blockdiagram of a tracing control including the invention. A cross-sectionline 10 of a model 12 which lies in a tracing plane 14 is being tracedby a tracing finger 16. As indicated in the Fig.,

the tracing plane 14 is parallel to the coordinate plane defined by theX and Y axes. The tracing finger I6 is part of a tracing head 1 18 whichis mounted on a machine (not shown) in a standard manner. The tracinghead 18 contains transducers (not shown) producing X axis, Y axis and Zaxis deflection signals on the output lines 20, 22 and 24, respectively.A deflection summing circuit 26 contained in the tracing control 28produces a total deflection signal on an output line 30 and a tracingplane deflection signal on an output line 32. A hang free to nulladjustment circuit 34 modifies the total deflection signal by a hangfree to null bias to produce a total" tracing error signal. This causesthe tracing control to null out or stabilize the tracing finger in aposition which is displaced from the mechanical null position.Consequently, the tracing head may distinguish between overdeflectionand underdeflection. This technique is well-known in the art. Aquadrature error generator 36 is responsive to the tracing error signalto produce, on output line 40, a quadrature error signal representing atracing error in the tracing plane perpendicular to the surface of themodel 12 at the tracing point. In other words, this signal represents aquadrature vector defining the distance and direction the tracing fingeris displaced form the hang free to null position. A feed rate commandgenerator 38 produces, on output line 42, a feed rate command ratesignal representing a predetermined velocity in the tracing planetangent to the surface of the model 12 at the tracing point. This signalrepresents a feed rate vector defining the direction and magnitude ofthe commanded velocity.

As mentioned earlier, there are several conditions which will skew thefeed rate vector from its tangent position. This produces a quadratureerror which the prior art systems did not automatically eliminate. Thepresent invention discloses a feed rate steering control 44 which isresponsive to the quadrature error signal and the feed rate commandsignal. The feed rate steering control 44 automatically rotates the feedrate vector to its ideal tangent position as a function of thequadrature error signal thereby holding the quadrature error signal at asubstantially zero value. The corrected feed rate command signal on line45 and the quadrature error signal are inputs to X-axis and Y-axiscontrol generators 46 and.48, respectively. The control generatorsreduce the input signals to the appropriate coordinate axis componentsand produce drive signals from the tracing control to the correspondingdriving mechanisms for moving the machine in a manner causing thetracing finger to accurately trace the cross section of the model 12 ina tracing place 14.

FIG. 2 is block diagram illustrating the basic components of theinvention. An error integrator 50 and feed rate correction circuit 52combine to form a feed rate steering control. The quadrature errorsignal on line 40 is an input to the error integrator 50 which producesa control signal having a magnitude that is a function of the timeaverage value of the quadrature error signal. The control signal has asign that is dependent on the direction of the quadrature error. A phasemodulationcircuit 54 is responsive to the control signal and produces'asteering signal having a magnitude that is a function of the controlsignal magnitudethat is a function of the control signal magnitude and aphase angle that is shifted 90 out of phase with the feed rate commandsignal. The phase shift occurs in a direction defined by the sign of thecontrol signal. A summing circuit 56 is responsive to the steeringsignal and the feedrate command signal and sums said signals to producea corrected feed rate command signal. The corrected command signalrepresents a feed rate vector having a magnitude equal to thepredetermined feed rate value and direction coincident with the tangentto the model at the tracing point.

FIG. 3 is a detailed schematic diagram of the invention. The quadratureerror signal on line 40 is input to an inverter amplifier 58 containedin the error integrator 50. A quadrature direction signal is input online 60 to a coil 62 of a flux module. The normally open contacts 66 andnormally closed contacts 64 are operative to switch the quadrature errorsignal or the inverse thereof as a function of the direction of thequadrature error signal. Consequently, the quadrature error or itsinversion is an input to an integrating amplifier 68, which integratesthe quadrature error signal. After the output of amplifier 68 passesthrough the voltage divider comprised of resistors 70 and 72, a controlsignal is produced from the integrator 50. The control signal ismodulated onto a carrier by multiplication in the carrier circuit 74with a multiplier signal out of phase with the command signal. Thecarrier signal is created by shifting the phase of the command signal inthe 90 phase shift circuit 76. The product of the multiplication is asteering signal having an amplitude and phase relation to the carriersignal as a function of the amplitude and sign, respectively, of thecontrol signal. The steering signal is an input to a resistive summingnetwork 78 contained in the summing circuit 56. The sum of the steeringsignal and the feed rate command signal passes through an amplifier 80,and the summing circuit 56 produces a corrected feed rate command signalon the output line 45.

While the invention has been illustrated in some detail according to thepreferred embodiments shown in the accompanying drawings and while thepreferred illustratedembodiments have been described in some detail,there is no intention to thus limit the invention to such details. Onthe contrary, it is intended to cover all modifications, alterations andequivalents falling within the spirit and scope of the appended claims.

What is claimed is:

1. An electronic tracing control comprised in part of apparatus forproducing a quadrature error signal and a feed rate command signal,wherein the improvement comprises:

a. means responsive to the quadrature error signal for producing acontrol signal as function of the time average value of the quadratureerror signal; and

b. means responsive to the control signal and the feed rate commandsignal for steering the feedrate command signal as a function of thecontrol signal to maintain the quadrature error signal at asubstantially zero value.

2. An electronic tracing control comprised in part of apparatus forproducing an error signal representing an erroneous deflection in adirection perpendicular to a model surface at a tracing point and acommand signal representing a predetermined tracing velocity oriented ata small angle to a tangent to the model surface at the tracing point,wherein the improvement comprises:

' a. means responsive to the error signal for producing a control signalas a function of the time average value of the error signal; and

b. means responsive to the control signal and the command signal forproducing a corrected command signal representing a velocity in adirection coincident with the tangent to the model surface at thetracing point, whereby said error signal is maintained at asubstantially zero value.

3. An electronic tracing control comprised in part of apparatus forproducing an error signal representing erroneous deflections in adirection perpendicular to a model surface at a tracing point and acommand signal representing a predetermined tracing velocity oriented ata small angle to a tangent to the model surface at the tracing point,wherein the improvement comprises:

a. means responsive to the error signal for integrating the error signalto produce a control signal; means responsive to the control signal forproducing a steering signal modulated as a function of the controlsignal and 90 out of phase with the command signal; and c. means forreceiving and summing the steering signal and the command signal toproduce a corrected command signal defining a velocity in a directioncoincident with the tangent to the model 7 surface at the tracing point.

4. An electronic tracing control comprised in part of apparatus forproducing an error signal representing erroneous deflections in adirection perpendicular to a model surface at a tracing point, a commandsignal representing a predetermined velocity along a line intersectingat a small angle a tangent to the model surface at the tracing point anddirection signal representing the direction of the velocity along saidline, wherein the improvement comprises:

a. an inverting amplifier responsive to the error signal for producingan inverted error signal;

b. a switching circuit responsive to the direction signal, the errorsignal and the inverted error signal for selectively producing the errorsignal and the inverted error signal as a function of the direction ofthe predetermined velocity;

c. an integrating amplifier connected to the switching circuit andproducing a control signal;

(1. a phase shift circuit responsive to the command signal for producinga reference signal 90 degrees out of phase with the command signal;

e. a multiplier circuit connected to the phase shift circuit and theintegrating amplifier for producing a steering signal; and

f. a summing circuit responsive to the steering signal and the commandsignal for summing said signal and producing a corrected command signal.

e. a multiplier circuit connected to the phase shift 0- circuit and theintegrating amplifier for producing a steering signal; and

f. a summing circuit responsive to the steering signal and the commandsignal for summing said signal and producing a corrected command signal.

1. An electronic tracing control comprised in part of apparatus forproducing a quadrature error signal and a feed rate command signal,wherein the improvement comprises: a. means responsive to the quadratureerror signal for producing a control signal as function of the timeaverage value of the quadrature error signal; and b. means responsive tothe control signal and the feed rate command signal for steering thefeedrate command signal as a function of the control signal to maintainthe quadrature error signal at a substantially zero value.
 1. Anelectronic tracing control comprised in part of apparatus for producinga quadrature error signal and a feed rate command signal, wherein theimprovement comprises: a. means responsive to the quadrature errorsignal for producing a control signal as function of the time averagevalue of the quadrature error signal; and b. means responsive to thecontrol signal and the feed rate command signal for steering thefeedrate command signal as a function of the control signal to maintainthe quadrature error signal at a substantially zero value.
 2. Anelectronic tracing control comprised in part of apparatus for producingan error signal representing an erroneous deflection in a directionperpendicular to a model surface at a tracing point and a command signalrepresenting a predetermined tracing velocity oriented at a small angleto a tangent to the model surface at the tracing point, wherein theimprovement comprises: a. means responsive to the error signal forproducing a control signal as a function of the time average value ofthe error signal; and b. means responsive to the control signal and thecommand signal for producing a corrected command signal representing avelocity in a direction coincident with the tangent to the model surfaceat the tracing point, whereby said error signal is maintained at asubstantially zero value.
 3. An electronic tracing control comprised inpart of apparatus for producing an error signal representing erroneousdeflections in a direction perpendicular to a model surface at a tracingpoint and a command signal representing a predetermined tracing velocityoriented at a small angle to a tangent to the model surface at thetracing point, wherein the improvement comprises: a. means responsive tothe error signal for integrating the error signal to produce a controlsignal; b. means responsive to the control signal for producing asteering signal modulated as a function of the control signal and 90*out of phase with the command signal; and c. means for receiving andsumming the steering signal and the command signal to produce acorrected command signal defining a velocity in a direction coincidentwith the tangent to the model surface at the tracing point.